Sometimes I hear the squeal, but not the rump.
The belt contains rubber and esp. if cold, it's slippery.
Accelerating from idling stresses the belt and the engine is still calm enough to hear other noises.
Might happen at 120kph too, but then we can't hear.
I imagine the rump is caused by some worn out part. Perhaps the belt.
Or the pulley isn't aligned.
But 8700 miles isn't much for the Xciting variomatic, this should last at least double distance.